Cordless digital communications systems such as DECT, WDCT, Bluetooth, SWAP, WLAN IEEE802.11 require suitable receivers for wire-free reception of the radio-frequency signals which are transmitted via the air interface, which receivers produce a baseband signal with as little distortion as possible for the demodulator in a simple manner. In addition to high sensitivity, a high degree of integration, low costs, low power consumption as well as flexibility with regard to applicability to different digital communications systems are desirable in this case.
In present-day receiver designs for digitally frequency-modulated signals, traditional signal processing methods are used for demodulation and for signal detection. One method that is frequently used is based on the so-called limiter discriminator FM demodulator, in which the frequency-modulated signal is demodulated, for example by means of an analog coincidence demodulator with appropriate detection, after hard limiting of the generally complex bandpass signal.
Furthermore, there are receiver concepts in which the intermediate-frequency signal is converted to the digital domain with the aid of an AID converter, and the signal detection is carried out using digital signal processing methods. Such a method is described, by way of example, in DE 101 03 479.2. In comparison to the analog receiver design, a method such as this admittedly makes it possible to achieve qualitative signal detection improvements. However, this approach has the disadvantage that a complex A/D converter is required.